The influence of calcium intake by broiler breeders on bone development and egg characteristics

[摘要] English: 1. A study was conducted to investigate the effects of dietary Ca levels and feed restriction on the bone development of broiler breeder pullets up to 18 weeks of age. Six hundred and forty one-day-old Ross breeder pullets were randomly assigned to 4 treatment groups; namely 1.0% Ca (0.45% Pi), 1.5% Ca (0.7% Pi), 2.0% Ca (0.9% Pi) and 1.0% Ca (0.45% Pi). The first three treatments were feed restricted while the last treatment was fed ad lib. At 6, 12 and 18 weeks of age 20 pullets were randomly selected from each treatment and killed. Treatment effects on bone dimensions (length, width and weight), bone ash, Ca and P contents of tibia, mechanical properties (bone strength and stress) were investigated. Increasing dieta ry Ca levels had no significant (P>0.05) effect on bone measurements. As expected, all the bone measurements significantly (P<0.05) increased with age. Feed restriction significantly (P<0.05) reduced all the bone characteristics. The results suggested that 1.0% Ca (average 0.7 g/hen/day) is sufficient to support bone development and growth for feed restricted broiler breeder pullets up to 18 weeks of age. 2. One hundred and ninety eight Ross broiler breeder pullets were reared on restricted diets with 1.0, 1.5 and 2.0% Ca up to 22 weeks of age. The pullets in each experimental diet were further randomly divided into three treatments with 1.5, 2.5 and 3.5% dietary Ca (66 birds per treatment) fed from 23 to 60 weeks. At 35 and 60 weeks of age, 12 pullets per treatment were randomly selected and killed to obtain tibiae and humeri. Treatment effects on bone dimensions, bone ash, Ca and P content of tibia, mechanical properties, true cortical area (TCA) and percent bone were investigated. The 1.5% Ca diet resulte d in lower (P<.05) feed intake and body weight. Calcium level had no effect on bone dimensions, bone stress, ash content, Ca content of ash, TCA and percent bone. These results suggest that the 2.5% dietary Ca (4 g/hen/day) may be adequate to support bone development and growth of feed restricted broiler breeder pullets. 3. The broiler breeder pullets described in paragraph 2 were used to investigate the effects of three levels of dietary Ca (1.5, 2.5 and 3.5%) during the early lay period (23 to 35 weeks) on egg production and eggshell quality. Increasing dietary Ca level from 1.5 to 3.5% had no significant effect (P>.05) on egg production, egg weight, egg mass, egg surface area and egg contents. Increasing the level of Ca from 1.5 to 2.5% increased shell weight, shell weight per unit surface area, shell percentage and shell thickness. As anticipated, egg weight increased with age. The converse was true for egg production and eggshell parameters. It was concluded that a dietary Ca level of 2.5% and Ca intakes of 3.8, 3.9, and 3.5 g at weeks 27, 30 and 33, respectively were sufficient to sustain good eggshell quality of feed restricted broiler breeder hens. 4. The mentioned broiler breeder hens in paragraph 3 were fed three dietary Ca levels, 1.5, 2.5 and 3.5% from week 36 to 60. Regression analysis suggested that Ca level during the rearing period could positively influence eggshell quality during the later stages of lay (36 to 60 weeks). Increasing dietary Ca level from 1.5 to 2.5% during the laying period significantly (P<.05) increased egg production, egg weight, egg mass, shell weight, egg contents, egg surface area, shell percentage, shell weight per unit surface area and shell thickness. As anticipated, egg weight, shell weight, egg contents and egg surface area increased with age while egg production, egg mass, shell percentage and shell thickness declined. These results suggest that the 2.5% Ca (3.8 g/hen/day) is adequate to support egg production and to improve eggshell quality in feed restricted broiler breeder hens. 5. The effect of dietary Ca intake (1.5, 2.5 and 3.5% dietary Ca) on Ca retention of broiler breeder hens (30 per treatment) and the relationship between Ca retention and egg characteristics was investigated. Shell (r=0.27) and faecal (r=0.50) Ca excretions were significantly (P<.05) positively related to Ca intake of broiler breeders. Proportionally less of the Ca intake was used for eggshell formation as the intake of broiler breeders increased. It seems that a higher Ca intake was mainly accompanied by a higher Ca excretion through the faeces. The net effect of Ca intake and total Ca excretion was that the 2.5% Ca level (3.8 g Ca /hen/day) exhibit a significant (P<.05) higher Ca retention compared to 1.5% Ca. It was concluded from the results that 1.0% dietary Ca (0.7 g /pullet/day) is needed during the rearing period up to 22 weeks. Thereafter 2.5% Ca (3.5 to 4.0 g /hen/day) should be included in broiler breeder diets up to 60 weeks. The possible effect of Ca levels during the rearing period on eggshell quality needs further investigation.

[发布机构] University of the Free State